It is known to control the injection of fuel into internal combustion engines using an open-loop control circuit. In these conventional systems the injection time and the pulse width of the injection are determined from predefined values stored in the engine's electronic control unit. Although such systems exhibit acceptable performance, they are otherwise prone to defects typical of open loop control. For example, the flow characteristics of an injector in a diesel engine may change during time as a result of wear phenomena, thus the pulse width used for the injector will no longer supply the engine with the desired quantity of fuel, and in general the performance of the engine will be degraded, giving way to higher emissions, higher fuel consumption, increased noise and even the possibility of damage to the engine.
In order to improve such situation, more recent engine combustion concepts, for example diesel Premixed Charge Compression Ignition (PCCI) and gasoline Homogenous Charge Compression Ignition (HCCI), require closed-loop control of characteristic combustion parameters, such as Start-of-Combustion (SoC), 50% fuel mass fraction burned (MFB50), location of peak pressure (LPP) and other parameters, in order to stabilize combustion and reduce emission dispersion on a cylinder-individual basis. Mostly combustion phasing based on MFB50 is performed.
These parameters can be directly measured by means of combustion pressure sensors. These sensors are being developed for application in production engines in a configuration that uses one sensor per cylinder.
While this solution has the best control accuracy, one serious problem of this approach is the high cost of the pressure sensors and therefore also sensor thrifting has been considered, e.g., having only two pressure sensors per engine or even one sensor per cylinder bank and applying information derived from such pressure sensor(s) to control also the cylinder(s) without pressure sensor(s) in order to reduce total cost. This second approach results in a reduced number of sensors per engine and gives way to closed-loop control of “lead cylinders” with pressure sensors and subordinated open-loop control of non-sensed cylinders depending on “lead cylinders”.
The benefit of this approach is reduced cost; the approach is still acceptable for Euro5 emission control standard, but it has the drawbacks of limited controls quality, increased emission dispersion and in general it is not acceptable for the tighter standard Euro6.
A further known approach is based on crank-speed fluctuation measured with a standard crank-speed sensor used to closed-loop control combustion phasing on a gasoline HCCI engine. Still another approach uses a torque sensor that provides a crank-angle resolved torque pattern for each cylinder. Torque is related to the in-cylinder pressure during combustion.
U.S. patent application US 2008/0053405 discloses another approach, namely a method of performing feedback control of the operation of an internal combustion engine based on a signal obtained from a vibration sensor and a crankshaft angle sensor. The vibration sensor preferably used is a knock sensor traditionally applied in spark-ignition internal combustion engines to detect auto-ignition. In the method a voltage or charge signal from said vibration sensor is acquired multiple times during a window of engine rotation. These signals, after suitable filtering and adjusting operation, are squared to obtain unfiltered energy factor values which are low pass filtered to remove high frequency components to obtain filtered energy factor values. A vector of energy factors can be computed as a function of crank angle degree over a particular window of engine rotation of interest. Based on the energy factor vector, combustion phasing can be estimated. Such method however mainly gives information on the start of combustion, because the vibration sensor substantially picks up vibrations associated with Start of Combustion (Soc) pulses for each cylinder.
At least one aim of the invention is therefore to provide for a method and a device for closed-loop combustion control within an internal combustion engine that improves the combustion phasing of the engine, while at the same time has reduced costs with respect to prior art methods. A further aim of the invention is to provide a reliable method for closed-loop combustion control which does not require a powerful hardware to be implemented. In addition, other aims, desirable features, and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.